1. Field of the Invention
This invention relates a method of fixing a cylindrical optical part and an electric part, and more particularly to a method of fixing on a substrate a cylindrical optical part which includes a lens, an optical semiconductor element having a light emitting portion or a light receiving portion located substantially at a focus position of the lens, and a terminal.
2. Description of the Related Art
When an optical communication system is to be constructed, various optical devices are required including an optical switch, an optical coupler and an optical beam combining/splitting filter. One of the basic forms of optical devices is a bulk type wherein various optical parts are placed on and fixed to a substrate having a flat face. An optical transmitter-receiver of the bulk type which can be used in bi-directional optical communications includes, for example, a fiber collimator having an end portion of an optical fiber and a collimation or condenser lens fixedly carried thereon, a glass block having a filter film thereon, a PD (photodiode) collimator having a PD chip and a condenser lens fixedly carried thereon, and LED (light emitting diode) collimator or an LD (laser diode) collimator having an LED chip or an LD chip and a collimation lens fixedly carried thereon, and parts of an electric circuit or the like, all mounted on a substrate. In such an optical device, relative positions of individual optical parts placed on and fixed to a substrate have a direct influence on optical coupling efficiency. Accordingly, the individual optical parts must necessarily be fixed in position with a high degree of accuracy. Meanwhile, from the aspect of manufacturing technology, a photo-semiconductor collimator such as a PD collimator or an LED collimator is required not only to be highly accurate in terms of mechanical fixation but also to be readily connect to an electric circuit. Further, in an optical device of the type mentioned, optical parts for optically forming a light path and electric parts for forming an electric circuit are mounted on the same substrate due to a demand for reduction in size of an apparatus and for improvement in S/N ratio. A need exists for a method of fixing such optical parts and electric parts with a high degree of reliability on a substrate.
An optical part such as a PD collimator or an LED collimator commonly has a cylindrical configuration. According to an exemplary one of the known methods of fixing such cylindrical optical or electric parts on a substrate, optical and electric parts are placed on a substrate with a solder layer interposed therebetween. Then, a heating block made of, as, for example, copper is pressed against a rear face of the substrate to melt the solder layer, and thereafter the molten solder is left until it is solidified, thereby collectively fixing the optical and electric parts to the substrate by soldering. In this instance, in order to achieve positioning of the optical parts with a high degree of accuracy, for example, a positioning jig having a V-shaped groove or grooves formed thereon is pressed against the cylindrical optical parts from the side opposite to the substrate to position the optical parts. Meanwhile, the heating block is placed on a hot plate heated to 240.degree. to 250.degree. C. so that heat may be transmitted by heat conduction to the substrate and the solder layer by way of the heating block thereby to collectively fix the optical parts and the electric parts by soldering.
However, according to the conventional soldering fixing method, terminals of the optical parts cannot be fixed simultaneously with mechanical fixation of the optical parts to the substrate. Thus, after the optical parts are fixed to the substrate by soldering, the terminals of the optical parts are bent until ends thereof are contacted with a wiring pattern formed on the substrate. Then, the terminals are connected to the wiring pattern by means of a soldering iron after the substrate has been heated by the hot plate to a temperature at which the mechanically soldered portions may not be melted, for example, to 100.degree. C.
With such conventional fixing method, however, since mechanical fixation and electrical connection of the cylindrical optical parts must necessarily be carried out separately, there is a problem that the manufacturing operation process is complicated. To the contrary, if heating by means of the hot plate in electrical connection is omitted in order to simplify the process, where a ceramic substrate is employed, there is a problem that a crack may occur in the substrate or electric connection may become uncertain due to local heating by means of the soldering iron.
Meanwhile, such a conventional collective soldering fixing method of optical parts and electric parts as described above which utilizes a hot plate and a heating block has a disadvantage that, since generally the heat capacity of optical parts is very great compared with the heat capacity of electric parts, if heat of the hot plate is transmitted to a substrate using a heating block of the same material in order to fix the electric parts sufficiently firmly to the substrate, then an excessively large amount of heat will be applied to the electric parts. In other words, there is a disadvantage that, since the electric parts have a longer thermal load period of time at a temperature at which solder is melted, an excessively large amount of heat is applied to the electric parts, which is not preferable for the reliability of the electric parts.